Piezoelectric motor control method and robot

Abstract

To provide a piezoelectric motor control method and a robot that can rotate a driven body with excellent energy efficiency.SOLUTION: A method controls a piezoelectric motor including a driven body that rotates around a rotation axis, and a plurality of piezoelectric vibrators that rotates the driven body by transmitting driving force to the driven body. The plurality of piezoelectric vibrators includes a first piezoelectric vibrator and a second piezoelectric vibrator having a larger distance from the rotation axis than the first piezoelectric vibrator. In a case where the driven body is accelerated, if a rotational speed of the driven body is less than a first speed, the driven body is rotated by the driving force of the second piezoelectric vibrator, and when the rotational speed of the driven body is equal to or more than the first speed, the driven body is rotated by the driving force of the first piezoelectric vibrator.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a control method for a piezoelectric motor and a robot. [Background technology]

[0002] For example, Patent Document 1 discloses a vibration actuator having three vibrators arranged at equal intervals on the same circumference, and a ring-shaped driven body that rotates when driven by the three vibrators. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-068112 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the vibration actuator of Patent Document 1, the three vibrator parts are located on the same circumference. Therefore, if the diameter of the driven body is large, the vibration actuator is suitable for high torque / low speed, and conversely, if the diameter of the driven body is small, the vibration actuator is suitable for low torque / high speed. Therefore, it is difficult to drive with excellent energy efficiency over a wide speed range. [Means for solving the problem]

[0005] The method for controlling a piezoelectric motor of the present invention includes: a plurality of piezoelectric vibrators that transmit a driving force to the driven body to rotate the driven body; the plurality of piezoelectric vibrators include a first piezoelectric vibrator and a second piezoelectric vibrator that is distant from the rotation axis greater than the first piezoelectric vibrator; When accelerating the driven body, When the rotation speed of the driven body is less than a first speed, the driven body is rotated by a driving force of the second piezoelectric vibrator; When the rotation speed of the driven body is equal to or higher than the first speed, the driven body is rotated by the driving force of the first piezoelectric vibrator.

[0006] The robot of the present invention includes a first member and a second member which are interconnected; and a piezoelectric motor whose drive is controlled by the above-mentioned control method, and which displaces the second member relative to the first member. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a piezoelectric motor according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a front view showing a piezoelectric driving device of the piezoelectric motor. [Diagram 3] 2 is a front view showing a piezoelectric vibrator included in the piezoelectric driving device. FIG. [Figure 4] FIG. 2 is a plan view of the piezoelectric driving device as viewed along the rotation axis. [Diagram 5] FIG. 4 is a diagram showing a drive signal applied to a piezoelectric vibrator. [Figure 6] FIG. 4 is a front view showing a driving state of the piezoelectric vibrator. [Figure 7] FIG. 13 is a diagram illustrating a method for controlling a piezoelectric motor. [Figure 8] FIG. 13 is a diagram illustrating a method for controlling a piezoelectric motor. [Figure 9] 10A to 10C are diagrams illustrating a method for controlling a piezoelectric motor according to a second embodiment. [Figure 10] 13A to 13C are diagrams illustrating a method for controlling a piezoelectric motor according to a third embodiment. [Figure 11] FIG. 11 is a perspective view showing a robot according to a fourth embodiment of the present invention. [Figure 12] 4 is a cross-sectional view showing a joint portion between a first arm and a second arm. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a piezoelectric motor control method and a robot according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

[0009] First Embodiment FIG. 1 is a cross-sectional view showing a piezoelectric motor according to a first embodiment of the present invention. FIG. 2 is a front view showing a piezoelectric drive device included in the piezoelectric motor. FIG. 3 is a front view showing a piezoelectric vibrator included in the piezoelectric drive device. FIG. 4 is a plan view of the piezoelectric drive device viewed from a direction along the rotation axis. FIG. 5 is a diagram showing a drive signal applied to the piezoelectric vibrator. FIG. 6 is a front view showing a driven state of the piezoelectric vibrator. FIGS. 7 and 8 are each a diagram showing a control method of a piezoelectric motor.

[0010] For ease of explanation, the rotor side of the piezoelectric vibrator is also referred to as the "tip side" and the side opposite the rotor is also referred to as the "base side". In addition, the three mutually orthogonal axes that are the coordinate axes specific to the piezoelectric vibrator are the X-axis, Y-axis, and Z-axis, and the direction along the X-axis is also referred to as the X-axis direction, the direction along the Y-axis is also referred to as the Y-axis direction, and the direction along the Z-axis is also referred to as the Z-axis direction. The arrow side of each axis is also referred to as the "plus side", and the side opposite the arrow is also referred to as the "minus side". In this specification, less than / greater than and less than / greater than are synonymous.

[0011] 1 includes a base 200, a rotor 300 as a driven body rotatable about a rotation axis O relative to the base 200, a piezoelectric driving device 400 that rotates the rotor 300 about the rotation axis O, an encoder (not shown) that detects the amount of rotation of the rotor 300, and a control device 600 that controls the driving of the piezoelectric driving device 400. In such a piezoelectric motor 100, the piezoelectric driving device 400 is driven under the control of the control device 600, and a driving force generated by the piezoelectric driving device 400 is transmitted to the rotor 300, causing the rotor 300 to rotate about the rotation axis O.

[0012] The rotor 300 is supported by the base 200 via a bearing B, and is rotatable around a rotation axis O relative to the base 200. The rotor 300 is annular about the rotation axis O, and has an inner periphery 310 and an outer periphery 320. The base 200 has two contact portions 330 and 340 arranged on its upper surface. The contact portion 330 is annular about the rotation axis O, and is arranged along the inner periphery 310. The contact portion 340 is annular about the rotation axis O, and is arranged along the outer periphery 320. The piezoelectric drive device 400 contacts the two contact portions 330 and 340.

[0013] The piezoelectric driving device 400 has a plurality of piezoelectric vibrators 410 and a biasing member 490 that biases each of the piezoelectric vibrators 410 toward the rotor 300. As shown in FIG. 2, each of the piezoelectric vibrators 410 has a vibrating portion 411, a supporting portion 412 that supports the vibrating portion 411, a connecting portion 413 that connects the vibrating portion 411 and the supporting portion 412, and a convex transmitting portion 414 that transmits the vibration of the vibrating portion 411 to the rotor 300.

[0014] As shown in FIG. 3, the vibration part 411 has a thickness direction in the Z-axis direction and is a plate-like shape extending in the XY plane including the X-axis and the Y-axis. In addition, the vibration part 411 has a longitudinal shape with the Y-axis direction as a longitudinal direction in a plan view, and particularly a rectangular shape in this embodiment. However, the shape of the vibration part 411 is not particularly limited as long as it can perform its function. In addition, the vibration part 411 has driving piezoelectric elements 420A to 420F and a detection piezoelectric element 420G that detects the vibration of the vibration part 411. In the center of the vibration part 411, the piezoelectric elements 420C and 420D are arranged side by side in the Y-axis direction. In addition, the piezoelectric elements 420A and 420B are arranged side by side in the Y-axis direction on the positive side of the X-axis direction of the piezoelectric elements 420C and 420D, and the piezoelectric elements 420E and 420F are arranged side by side in the Y-axis direction on the negative side of the X-axis direction. These piezoelectric elements 420A to 420F each expand and contract in the Y-axis direction when electricity is applied. However, the number and arrangement of the driving piezoelectric elements are not particularly limited as long as they can excite the vibration portion 411 to produce the desired vibration.

[0015] The detection piezoelectric element 420G is disposed between the piezoelectric elements 420C and 420D. The piezoelectric element 420G receives an external force corresponding to the vibration of the vibration part 411, and outputs a detection signal corresponding to the received external force. Therefore, the vibration state of the vibration part 411 can be detected based on the detection signal output from the piezoelectric element 420G. The number and arrangement of the detection piezoelectric elements are not particularly limited as long as they can detect the vibration of the vibration part 411. The detection piezoelectric elements may be omitted.

[0016] These piezoelectric elements 420A to 420F are configured, for example, by sandwiching a piezoelectric body between a pair of electrodes. The constituent material of the piezoelectric body is not particularly limited, and for example, piezoelectric ceramics such as lead zirconate titanate (PZT), barium titanate, lead titanate, potassium niobate, lithium niobate, lithium tantalate, sodium tungstate, zinc oxide, barium strontium titanate (BST), strontium bismuth tantalate (SBT), lead metaniobate, lead scandium niobate, etc. may be used as the piezoelectric body, in addition to the above-mentioned piezoelectric ceramics, polyvinylidene fluoride, quartz, etc. may also be used. The method of forming the piezoelectric body is not particularly limited, and it may be formed from a bulk material, or may be formed using a sol-gel method or a sputtering method.

[0017] The transmission part 414 is provided at the tip of the vibration part 411, and protrudes from the vibration part 411 to the negative side in the Y-axis direction. The transmission part 414 contacts the abutment parts 330, 340 of the rotor 300. Therefore, the vibration of the vibration part 411 is transmitted to the rotor 300 via the transmission part 414.

[0018] The configuration of the piezoelectric vibrator 410 has been described above. As shown in FIG. 1 and FIG. 4, the plurality of piezoelectric vibrators 410 include a first piezoelectric vibrator 410A and a second piezoelectric vibrator 410B. The first piezoelectric vibrator 410A is disposed opposite the contact portion 330, and the transmission portion 414 thereof is in contact with the contact portion 330. On the other hand, the second piezoelectric vibrator 410B is disposed opposite the contact portion 340, and the transmission portion 414 thereof is in contact with the contact portion 340. Therefore, the separation distance Db between the second piezoelectric vibrator 410B and the rotation axis O is larger than the separation distance Da between the first piezoelectric vibrator 410A and the rotation axis O. In other words, Db>Da.

[0019] As shown in FIG. 4, the first piezoelectric vibrators 410A are arranged at equal intervals around the rotation axis O along the contact portion 330. Similarly, the second piezoelectric vibrators 410B are arranged at equal intervals around the rotation axis O along the contact portion 340. In this manner, by arranging the first piezoelectric vibrators 410A and the second piezoelectric vibrators 410B in plurality, a larger driving force can be generated. Note that the number of the first piezoelectric vibrators 410A and the second piezoelectric vibrators 410B is not particularly limited and may be one. Also, the number of the first piezoelectric vibrators 410A and the second piezoelectric vibrators 410B may be the same or different. Since the inner circumference 310 is shorter than the outer circumference 320, in this embodiment, the number of the first piezoelectric vibrators 410A (10 pieces) is smaller than the number of the second piezoelectric vibrators 410B (20 pieces).

[0020] As shown in FIG. 2, the biasing member 490 is disposed for each piezoelectric vibrator 410. The biasing member 490 biases the piezoelectric vibrator 410 toward the rotor 300, and presses the transmission section 414 against the contact sections 330 and 340. The biasing member 490 has a holding section 491 that holds the support section 412 of the piezoelectric vibrator 410, a base 492 that fixes the piezoelectric vibrator 410 to the base 200, and a pair of spring groups 493 and 494 that connect the holding section 491 and the base 492. The biasing member 490 is fixed to the base 200 with the spring groups 493 and 494 deflected, and biases the piezoelectric vibrator 410 toward the contact sections 330 and 340 by utilizing the restoring forces of the spring groups 493 and 494. However, the configuration of the biasing member 490 is not particularly limited.

[0021] The control device 600 is, for example, a computer, and has a processor for processing information, a memory communicably connected to the processor, and an external interface. In addition, a program executable by the processor is stored in the memory, and the processor reads and executes the program stored in the memory. Such a control device 600 receives a command from a host computer (not shown) and drives each piezoelectric vibrator 410 based on the command. In this embodiment, all the first piezoelectric vibrators 410A are collectively controlled, and all the second piezoelectric vibrators 410B are collectively controlled. This simplifies the device configuration. However, this is not limited to this, and for example, all the piezoelectric vibrators 410 may be controlled independently. In addition, for example, the first piezoelectric vibrators 410A may be divided into a plurality of groups, and each group may be controlled independently. Similarly, the second piezoelectric vibrators 410B may be divided into a plurality of groups, and each group may be controlled independently.

[0022] For example, when the drive signal V1 shown in FIG. 5 is applied to the piezoelectric elements 420A and 420F, the drive signal V2 is applied to the piezoelectric elements 420C and 420D, and the drive signal V3 is applied to the piezoelectric elements 420B and 420E, as shown in FIG. 6, the vibration unit 411 vibrates in a stretching and contracting manner in the Y-axis direction while vibrating in a bending manner in the Z-axis direction, and these vibrations are combined to cause the tip of the transmission unit 414 to perform an elliptical motion that describes an elliptical orbit in the counterclockwise direction as shown by the arrow A1. Then, the elliptical motion of the transmission unit 414 sends out the rotor 300, and the rotor 300 rotates forward as shown by the arrow B1. When the waveforms of the drive signals V1 and V3 are switched, the rotor 300 rotates in the reverse direction. Note that the meaning of "elliptical motion" includes not only a motion whose locus coincides with an ellipse, but also a motion whose locus is slightly deviated from an ellipse, such as a circle or an oval.

[0023] For convenience of explanation, the stretching vibration of vibrating part 411 in the Y-axis direction is also referred to as "reciprocating vibration", and the bending vibration in the X-axis direction is also referred to as "bending vibration". The reciprocating vibration is excited by application of drive signal V2 to piezoelectric elements 420C and 420D, and the bending vibration is excited by application of drive signals V1 and V3 to piezoelectric elements 420A, 420B, 420E, and 420F. Therefore, the reciprocating vibration is controlled by drive signal V2, and the bending vibration is controlled by drive signals V1 and V3.

[0024] Next, a drive control method for piezoelectric motor 100 by control device 600 will be described taking as an example an example of rotationally moving rotor 300 from rotational position θ0 to rotational position θ1 as shown in Fig. 7. During the rotational movement from rotational position θ0 to rotational position θ1, there are an acceleration region Q1 in which rotor 300 is accelerated from a stopped state to a target maximum speed Vm, a constant speed region Q2 in which rotor 300 is maintained at the target maximum speed Vm, and a deceleration region Q3 in which rotor 300 is decelerated from the target maximum speed Vm to a stopped state.

[0025] Here, as described above, the separation distance Db between the second piezoelectric vibrator 410B and the rotation axis O is larger than the separation distance Da between the first piezoelectric vibrator 410A and the rotation axis O. Therefore, if the power consumption is the same (that is, if the amplitudes of the drive signals V1, V2, and V3 are the same), the second piezoelectric vibrator 410B can rotate the rotor 300 with a larger torque than the first piezoelectric vibrator 410A, and conversely, the first piezoelectric vibrator 410A can rotate the rotor 300 at a higher speed than the second piezoelectric vibrator 410B. Therefore, for example, like a transmission for an automobile, by selecting the piezoelectric vibrator 410 to be driven according to the required rotation speed and required torque from the first piezoelectric vibrator 410A or the second piezoelectric vibrator 410B, an optimal driving state can be selected, and excellent driving efficiency can be exhibited.

[0026] [Acceleration region Q1] First, the control device 600 vibrates the second piezoelectric vibrator 410B in an elliptical manner. This allows the rotor 300 to rotate with a large torque, and the rotor 300 in a stopped state can be smoothly accelerated. In addition, the rotor 300 can be rotated with higher energy efficiency than when the elliptical vibration of the first piezoelectric vibrator 410A is used, and the piezoelectric motor 100 can be driven with less power consumption.

[0027] Each piezoelectric vibrator 410 is pressed against the contact parts 330, 340 by the biasing member 490. Therefore, if the first piezoelectric vibrator 410A remains stopped, the first piezoelectric vibrator 410A may act as a brake and impede the acceleration of the rotor 300. Therefore, the control device 600 vibrates the first piezoelectric vibrator 410A back and forth. As a result, the transmission part 414 of the first piezoelectric vibrator 410A repeatedly comes into contact with and separates from the contact part 330, and the brake is essentially released. Therefore, the rotor 300 can be smoothly accelerated by the elliptical vibration of the second piezoelectric vibrator 410B, and energy loss is reduced.

[0028] When the rotation speed, i.e., angular velocity, of the rotor 300 becomes equal to or higher than a first speed Vr1 set in advance, the control device 600 switches the piezoelectric vibrator 410 that drives the rotor 300 from the second piezoelectric vibrator 410B to the first piezoelectric vibrator 410A. That is, when the rotation speed of the rotor 300 becomes equal to or higher than the first speed Vr1, the vibration of the first piezoelectric vibrator 410A is shifted from reciprocating vibration to elliptical vibration, and the vibration of the second piezoelectric vibrator 410B is shifted from elliptical vibration to reciprocating vibration. The rotation speed of the rotor 300 can be detected using the output of an encoder (not shown). This allows the rotor 300 to rotate at a higher speed, and the rotor 300 can be accelerated smoothly. In addition, the rotor 300 can be rotated with higher energy efficiency than when the rotor 300 is accelerated directly using the elliptical vibration of the second piezoelectric vibrator 410B, and the piezoelectric motor 100 can be driven with less power consumption.

[0029] The vibration of second piezoelectric vibrator 410B is shifted from elliptical vibration to reciprocating vibration for the same reason as described above, that is, to prevent second piezoelectric vibrator 410B from acting as a brake.

[0030] The first speed Vr1 is not particularly limited, and can be appropriately set based on the values ​​of the separation distances Da and Db so as to improve energy efficiency. The first speed Vr1 may be constant, or may change according to, for example, the specified acceleration. For example, the control device 600 may increase the first speed Vr1 as the specified acceleration increases. This allows the second piezoelectric vibrator 410B to be used up to a higher speed range, so that the acceleration can be accelerated to a higher speed more rapidly.

[0031] In this embodiment, when the piezoelectric vibrator 410 that drives the rotor 300 is switched from the second piezoelectric vibrator 410B to the first piezoelectric vibrator 410A, a time period T1 is provided during which both the first and second piezoelectric vibrators 410A and 410B elliptical vibrate. That is, even if the rotation speed of the rotor 300 becomes equal to or higher than the first speed Vr1, the second piezoelectric vibrator 410B continues to elliptical vibrate even after the first piezoelectric vibrator 410A is elliptical vibrated for a predetermined time or until the rotation speed of the rotor 300 becomes equal to or higher than a predetermined value. By providing such a time period T1, it is possible to switch from the second piezoelectric vibrator 410B to the first piezoelectric vibrator 410A without interrupting the power. Therefore, it is possible to smoothly switch the power.

[0032] After the piezoelectric vibrator 410 that drives the rotor 300 is switched to the first piezoelectric vibrator 410A, the rotor 300 is accelerated up to a target maximum speed Vm by the elliptical vibration of the first piezoelectric vibrator 410A.

[0033] [Constant velocity region Q2] In the constant speed region Q2, the control device 600 maintains the rotational speed of the rotor 300 at the target maximum speed Vm.

[0034] [Deceleration area Q3] In the deceleration region Q3, the rotor 300 is decelerated in the reverse order to the acceleration region Q1 described above. First, the control device 600 gradually reduces the amplitude of the elliptical vibration of the first piezoelectric vibrator 410A to decelerate the rotor 300. Then, when the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the piezoelectric vibrator 410 that drives the rotor 300 is switched from the first piezoelectric vibrator 410A to the second piezoelectric vibrator 410B. In other words, when the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the vibration of the second piezoelectric vibrator 410B is shifted from reciprocating vibration to elliptical vibration, and the vibration of the first piezoelectric vibrator 410A is shifted from elliptical vibration to reciprocating vibration. This allows the rotor 300 to rotate with a large torque, and the rotor 300 to be decelerated smoothly. Furthermore, the rotor 300 can be decelerated with high energy efficiency compared to the case where the rotor 300 is decelerated directly using the elliptical vibration of the first piezoelectric vibrator 410A, and the piezoelectric motor 100 can be driven with reduced power consumption.

[0035] The vibration of first piezoelectric vibrator 410A is shifted from elliptical vibration to reciprocating vibration for the same reason as described above, that is, to prevent first piezoelectric vibrator 410A from acting as a brake and causing unstable deceleration.

[0036] Here, in this embodiment, when the piezoelectric vibrator 410 that drives the rotor 300 is switched from the first piezoelectric vibrator 410A to the second piezoelectric vibrator 410B, a time period T2 is provided during which both the first and second piezoelectric vibrators 410A and 410B elliptical vibrate. That is, even if the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the elliptical vibration of the first piezoelectric vibrator 410A continues even after the second piezoelectric vibrator 410B is elliptical vibrated for a predetermined time from that time or until the rotation speed of the rotor 300 becomes equal to or lower than a predetermined value. By providing such a time period T2, it is possible to switch from the first piezoelectric vibrator 410A to the second piezoelectric vibrator 410B without interrupting the power. Therefore, it is possible to smoothly switch the power.

[0037] The second speed Vr2 is not particularly limited, and can be appropriately set based on the values ​​of the separation distances Da and Db so as to improve energy efficiency. The second speed Vr2 may be constant, or may change according to the specified acceleration, for example. For example, the control device 600 may increase the second speed Vr2 as the specified deceleration increases. This allows the second piezoelectric vibrator 410B to be used from a higher speed range, so that the speed can be decelerated more steeply from the higher speed range.

[0038] In addition, in this embodiment, the first speed Vr1 at which the second piezoelectric vibrator 410B is switched to the first piezoelectric vibrator 410A during acceleration and the second speed Vr2 at which the first piezoelectric vibrator 410A is switched to the second piezoelectric vibrator 410B during deceleration are the same, but are not limited to this and may be different.

[0039] After the piezoelectric vibrator 410 that drives the rotor 300 is switched to the second piezoelectric vibrator 410B, the amplitude of the elliptical vibration of the second piezoelectric vibrator 410B is gradually reduced, and when the rotor 300 reaches the rotation position θ1, the driving of both the first and second piezoelectric vibrators 410A and 410B is stopped. In a state in which the driving of the first and second piezoelectric vibrators 410A and 410B is stopped, the first and second piezoelectric vibrators 410A and 410B function as brakes, so that the rotation of the rotor 300 relative to the base 200 is prevented, and the position of the rotor 300 is maintained at the rotation position θ1. In other words, according to the piezoelectric motor 100, the piezoelectric vibrator 410 functions as both a driving source that rotates the rotor 300 and a brake that prevents the rotation of the rotor 300, so there is no need to provide a brake separately in addition to the driving source. Therefore, the piezoelectric motor 100 can be made smaller.

[0040] The drive control method of the piezoelectric motor 100 by the control device 600 has been described above. However, the drive control method of the piezoelectric motor 100 by the control device 600 is not limited to the above method. For example, if it is desired to rotate the rotor 300 with a larger torque regardless of acceleration, deceleration, or constant speed, the first and second piezoelectric vibrators 410A and 410B may be elliptical vibrated together. This allows the rotor 300 to rotate with a larger torque by cooperation of the first and second piezoelectric vibrators 410A and 410B. For example, in the example shown in FIG. 8, the first and second piezoelectric vibrators 410A and 410B are elliptical vibrated together in the entire acceleration region Q1 and the entire deceleration region Q3, and in the constant speed region Q2, the first piezoelectric vibrator 410A is elliptical vibrated and the second piezoelectric vibrator 410B is reciprocatingly vibrated.

[0041] Since Db>Da, if the first and second piezoelectric vibrators 410A, 410B are elliptical vibrated with the same amplitude, the angular velocity applied to the inner circumference side of the rotor 300 becomes larger than the angular velocity applied to the outer circumference side, so that the first piezoelectric vibrator 410A located on the inside acts like a brake, and the second piezoelectric vibrator 410B located on the outside is dragged by the rotor 300. This hinders the smooth rotation of the rotor 300, which may cause excessive wear of the rotor 300 and the transmission unit 414, or may cause a deterioration in drive efficiency.

[0042] Therefore, it is preferable to make the driving force of the first piezoelectric vibrator 410A smaller than that of the second piezoelectric vibrator 410B so that the angular velocities occurring on the inner circumference side and the outer circumference side of the rotor 300 are equal. For example, a method of making the driving force smaller is to make the voltage of the driving signals V1 and V3 applied to the first piezoelectric vibrator 410A smaller than the voltage of the driving signals V1 and V3 applied to the second piezoelectric vibrator 410B. As a result, the amplitude of the elliptical vibration of the first piezoelectric vibrator 410A becomes smaller than the amplitude of the elliptical vibration of the second piezoelectric vibrator 410B, and the driving force of the first piezoelectric vibrator 410A becomes smaller than the driving force of the second piezoelectric vibrator 410B. Therefore, the occurrence of the above-mentioned problems is suppressed, and the rotor 300 can be rotated smoothly.

[0043] Since the angular velocity is generally proportional to the voltage ratio of the drive signals V1 and V3, for example, the magnitude of the drive signals V1 and V3 applied to the first piezoelectric vibrator 410A may be determined based on the ratio of Db and Da. That is, the magnitude of the drive signals V1 and V3 applied to the first piezoelectric vibrator 410A may be set to about Da / Db, which is the magnitude of the drive signals V1 and V3 applied to the second piezoelectric vibrator 410B. This makes the angular velocities generated on the inner and outer circumferential sides of the rotor 300 almost equal, allowing the rotor 300 to rotate smoothly. This also makes it possible to suppress wear on the rotor 300 and the transmission unit 414, and to rotate the rotor 300 with high energy efficiency.

[0044] As described above, the control method of the piezoelectric motor includes the rotor 300 as a driven body rotating around the rotation axis O, and a plurality of piezoelectric vibrators 410 that rotate the rotor 300 by transmitting a driving force to the rotor 300, the plurality of piezoelectric vibrators 410 including a first piezoelectric vibrator 410A and a second piezoelectric vibrator 410B that is distant from the rotation axis O greater than the first piezoelectric vibrator 410A, and when accelerating the rotor 300, if the rotation speed of the rotor 300 is less than a first speed Vr, the rotor 300 is rotated by transmitting the driving force of the second piezoelectric vibrator 410B to the rotor 300, and if the rotation speed of the rotor 300 is equal to or greater than the first speed Vr, the rotor 300 is rotated by transmitting the driving force of the first piezoelectric vibrator 410A to the rotor 300. In this way, by selecting the piezoelectric vibrator 410 that drives the rotor 300 in accordance with the rotation speed of the rotor 300, the rotor 300 can be rotated with excellent energy efficiency.

[0045] As described above, the piezoelectric vibrator 410 has a vibration section 411 that vibrates when electricity is applied to the piezoelectric elements 420A to 420F, and a transmission section 414 that abuts against the rotor 300 and transmits the vibration of the vibration section 411 to the rotor 300. When transmitting a driving force to the rotor 300, the transmission section 414 is vibrated in an elliptical shape, and when not transmitting the driving force to the rotor 300, the transmission section 414 is vibrated back and forth in a direction approaching and moving away from the rotor 300. This makes it possible to suppress a decrease in the driving efficiency by making the piezoelectric vibrator 410 on the side not transmitting the driving force act as a brake.

[0046] As described above, when the rotor 300 accelerates, when the rotation speed of the rotor 300 reaches or exceeds the first speed Vr, the vibration of the first piezoelectric vibrator 410A is changed from a reciprocating vibration to an elliptical vibration, and the vibration of the second piezoelectric vibrator 410B is changed from an elliptical vibration to a reciprocating vibration. This allows the rotor 300 to accelerate with excellent energy efficiency.

[0047] As described above, the first piezoelectric vibrator 410A and the second piezoelectric vibrator 410B both undergo an elliptical vibration, and then the first piezoelectric vibrator 410A vibrates elliptically, and the second piezoelectric vibrator 410B vibrates back and forth. This allows the power to be switched from the second piezoelectric vibrator 410B to the first piezoelectric vibrator 410A without interruption. This allows for smooth switching of the power.

[0048] Furthermore, as described above, in a state in which both the first piezoelectric vibrator 410A and the second piezoelectric vibrator 410B are elliptical vibrating, the driving force of the first piezoelectric vibrator 410A is made smaller than the driving force of the second piezoelectric vibrator 410B. This makes the difference in angular velocity generated between the inner and outer circumferential sides of the rotor 300 small, preferably zero, and allows the rotor 300 to rotate smoothly with high energy efficiency.

[0049] As described above, when the rotor 300 is decelerating, when the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the vibration of the first piezoelectric vibrator 410A is changed from elliptical vibration to reciprocating vibration, and the vibration of the second piezoelectric vibrator 410B is changed from reciprocating vibration to elliptical vibration. This allows the rotor 300 to decelerate with excellent energy efficiency.

[0050] <Second embodiment> FIG. 9 is a diagram illustrating a method for controlling the piezoelectric motor according to the second embodiment.

[0051] The control method of the piezoelectric motor of this embodiment is the same as the control method of the piezoelectric motor of the first embodiment described above, except for the control method in the deceleration region Q3. In the following description, the present embodiment will be described focusing on the differences from the previous embodiment, and the description of the similarities will be omitted. In FIG. 9, the same reference numerals are used for the same configurations as the previous embodiment.

[0052] [Deceleration area Q3] As shown in FIG. 9, in the deceleration region Q3 of this embodiment, first, the control device 600 gradually reduces the amplitude of the elliptical vibration of the first piezoelectric vibrator 410A to decelerate the rotor 300. Then, when the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the second piezoelectric vibrator 410B is added to the piezoelectric vibrator 410 that drives the rotor 300. That is, when the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the vibration of the second piezoelectric vibrator 410B is shifted from reciprocating vibration to elliptical vibration while maintaining the vibration of the first piezoelectric vibrator 410A as elliptical vibration, and the rotor 300 is rotated by the cooperation of the first and second piezoelectric vibrators 410B. This allows the rotor 300 to rotate with a larger torque, and the rotor 300 can be decelerated by static friction force, so that the rotor 300 can be decelerated smoothly and at a high deceleration rate.

[0053] At or below the second speed Vr2, the driving force of the first piezoelectric vibrator 410A is made smaller than that of the second piezoelectric vibrator 410B so that the angular velocities occurring on the inner circumference side and the outer circumference side of the rotor 300 are equal. As a result, the amplitude of the elliptical vibration of the first piezoelectric vibrator 410A becomes smaller than that of the second piezoelectric vibrator 410B, and the driving force of the first piezoelectric vibrator 410A becomes smaller than that of the second piezoelectric vibrator 410B. Therefore, the occurrence of the problems described in the first embodiment is suppressed, and the rotor 300 can be rotated smoothly.

[0054] After the piezoelectric vibrator 410 that drives the rotor 300 is switched to the first and second piezoelectric vibrators 410A, 410B, the amplitude of the elliptical vibration of the first and second piezoelectric vibrators 410A, 410B is gradually reduced, and when the rotor 300 reaches the rotational position θ1, the driving of both the first and second piezoelectric vibrators 410A, 410B is stopped.

[0055] As described above, in the control method for the piezoelectric motor of this embodiment, the vibrations of both the first piezoelectric vibrator 410A and the second piezoelectric vibrator 410B are elliptical vibrations when the rotor 300 is decelerating. This allows the rotor 300 to rotate with a larger torque, and the rotor 300 can be decelerated smoothly and at a high deceleration rate.

[0056] The second embodiment can achieve the same effect as the first embodiment. However, the second embodiment is not limited to this, and for example, the rotor 300 may be rotated and decelerated by elliptical vibration of both the first and second piezoelectric vibrators 410A, 410B in the entire deceleration region Q3.

[0057] <Third embodiment> FIG. 10 is a diagram illustrating a method for controlling the piezoelectric motor according to the third embodiment.

[0058] The control method of the piezoelectric motor of this embodiment is the same as the control method of the piezoelectric motor of the first embodiment described above, except for the control method in the deceleration region Q3. In the following description, the present embodiment will be described with a focus on the differences from the previous embodiment, and the description of the similarities will be omitted. In FIG. 10, the same reference numerals are used for the same configurations as the previous embodiment.

[0059] [Deceleration area Q3] As shown in FIG. 10, in the deceleration region Q3 of this embodiment, first, the control device 600 gradually reduces the amplitude of the elliptical vibration of the first piezoelectric vibrator 410A to decelerate the rotor 300. Then, when the rotation speed of the rotor 300 becomes equal to or lower than the second speed Vr2, the driving of both the first and second piezoelectric vibrators 410A and 410B is stopped. This applies a brake to the rotor 300, and the rotor 300 can be decelerated. According to this method, since it is not necessary to energize the first and second piezoelectric vibrators 410A and 410B, it is possible to drive the piezoelectric motor 100 with low power consumption.

[0060] As described above, in the control method for the piezoelectric motor of this embodiment, when the rotor 300 is decelerating, the driving of the first piezoelectric vibrator 410A and the second piezoelectric vibrator 410B is stopped. This applies a brake to the rotor 300, and the rotor 300 can be decelerated. In addition, since it is not necessary to pass electricity to the first and second piezoelectric vibrators 410A and 410B, the piezoelectric motor 100 can be driven in a power-saving manner.

[0061] The third embodiment can also achieve the same effects as the first embodiment. However, the third embodiment is not limited to this, and for example, the driving of both the first and second piezoelectric vibrators 410A and 410B may be stopped in the entire deceleration region Q3.

[0062] <Fourth embodiment> Fig. 11 is a perspective view showing a robot according to a fourth embodiment of the present invention, Fig. 12 is a cross-sectional view showing a joint portion between a first arm and a second arm.

[0063] 11 is capable of performing operations such as supplying, removing, transporting, and assembling precision equipment and the parts that constitute the equipment. Such a robot 1000 is a six-axis articulated robot, and has a base 1100 that is fixed to the floor or ceiling, and a manipulator 1200 that is supported by the base 1100.

[0064] The manipulator 1200 is a robotic arm that moves with multiple degrees of freedom by having multiple interconnected arms, and has a first arm 1210 rotatably connected to the base 1100, a second arm 1220 rotatably connected to the first arm 1210, a third arm 1230 rotatably connected to the second arm 1220, a fourth arm 1240 rotatably connected to the third arm 1230, a fifth arm 1250 rotatably connected to the fourth arm 1240, a sixth arm 1260 rotatably connected to the fifth arm 1250, and an end effector 1270 attached to the sixth arm 1260.

[0065] Any one selected from the first to sixth arms 1210 to 1260 and the end effector 1270 can be the first member, and any one selected from the rest of the first members can be the second member. Also, for example, if the end effector 1270 has a plurality of relatively movable members, such as a pair of claws for gripping a workpiece, one of the claws can be the first member and the other claw can be the second member. In the illustrated configuration, the first arm 1210 is the first member R1, and the second arm 1220 is the second member R2.

[0066] The robot 1000 also includes a first arm rotation mechanism 1310 that is disposed at the joint between the base 1100 and the first arm 1210 and rotates the first arm 1210 relative to the base 1100, a second arm rotation mechanism 1320 that is disposed at the joint between the first arm 1210 and the second arm 1220 and rotates the second arm 1220 relative to the first arm 1210, a third arm rotation mechanism 1330 that is disposed at the joint between the second arm 1220 and the third arm 1230 and rotates the third arm 1230 relative to the second arm 1220, and a fourth arm rotation mechanism 1330 that is disposed at the joint between the third arm 1230 and the fourth arm 1230. 240 and rotates the fourth arm 1240 relative to the third arm 1230, a fifth arm rotating mechanism 1350 arranged at the joint between the fourth arm 1240 and the fifth arm 1250 and rotates the fifth arm 1250 relative to the fourth arm 1240, a sixth arm rotating mechanism 1360 arranged at the joint between the fifth arm 1250 and the sixth arm 1260 and rotates the sixth arm 1260 relative to the fifth arm 1250, and an end effector driving mechanism 1370 that drives the end effector 1270. The robot 1000 also has a robot control unit 1400 that controls the driving of the first to sixth arm rotating mechanisms 1310 to 1360 and the end effector driving mechanism 1370.

[0067] A piezoelectric motor 100 is mounted as a power source on some or all of the first to sixth arm rotation mechanisms 1310-1360 and the end effector drive mechanism 1370, and the corresponding first to sixth arms 1210-1260 and end effector 1270 are driven by the piezoelectric motor 100. In addition, the control method for the piezoelectric motor 100 described in the first to third embodiments is applied to control the piezoelectric motor 100, for example. Therefore, the robot 1000 can enjoy the effects of the control method for the piezoelectric motor 100 described above, and can be driven with excellent energy efficiency.

[0068] Here, as described above, the piezoelectric motor 100 has the first piezoelectric vibrator 410A and the second piezoelectric vibrator 410B as the piezoelectric vibrator 410. Therefore, the piezoelectric motor 100 also functions as a reducer by switching between the first piezoelectric vibrator 410A and the second piezoelectric vibrator 410B. In other words, the piezoelectric motor 100 also functions as a reducer. Therefore, as shown in FIG. 12, in the first arm rotation mechanism 1310, the base 200 is fixed to the first arm 1210, the rotor 300 is fixed to the second arm 1220, and no reducer is provided between the rotor 300 and the second arm 1220 to reduce the rotation of the rotor 300. Therefore, the first arm rotation mechanism 1310 can be made smaller. The same applies to the second to sixth arm rotation mechanisms 1320 to 1360 and the end effector drive mechanism 1370.

[0069] As described above, in the piezoelectric motor 100, the first and second piezoelectric vibrators 410A and 410B stop driving to prevent the rotor 300 from rotating and also function as a brake to maintain the relative positions of the connected arms. In other words, the first and second piezoelectric vibrators 410A and 410B also function as a brake to prevent the rotor 300 from rotating. Therefore, as shown in FIG. 12, the first arm rotation mechanism 1310 does not have a brake to prevent the rotor 300 from rotating, separate from the piezoelectric motor 100. Therefore, the first arm rotation mechanism 1310 can be made smaller. The same applies to the second to sixth arm rotation mechanisms 1320 to 1360 and the end effector drive mechanism 1370.

[0070] As described above, the robot 1000 has the first arm 1210 as the first member R1 and the second arm 1220 as the second member R2, which are interconnected, and the piezoelectric motor 100 that displaces the second arm 1220 relative to the first arm 1210. Therefore, the robot 1000 can enjoy the effects of the piezoelectric motor 100, and can be driven with excellent energy efficiency.

[0071] As described above, the piezoelectric motor 100 also functions as a reducer. Therefore, there is no need to provide a reducer separately from the piezoelectric motor 100, and the robot 1000 can be made smaller.

[0072] As described above, in the piezoelectric motor 100, the piezoelectric vibrator 410 also functions as a brake that stops the rotation of the rotor 300. Therefore, there is no need to provide a brake separately from the piezoelectric motor 100, and the robot 1000 can be made smaller.

[0073] The fourth embodiment as described above can also achieve the same effects as the first embodiment described above.

[0074] The piezoelectric motor control method and robot of the present invention have been described above based on the illustrated embodiment, but the present invention is not limited thereto, and the configuration of each part can be replaced with any configuration having a similar function. Any other configuration may be added to the present invention. The embodiments may be appropriately combined. In the above embodiment, the piezoelectric motor control method is applied to a robot, but the piezoelectric motor control method can also be applied to various electronic devices that require driving force other than robots, such as printers and projectors. [Explanation of symbols]

[0075] 100...piezoelectric motor, 200...base, 300...rotor, 310...inner circumference, 320...outer circumference, 330...contact portion, 340...contact portion, 400...piezoelectric driving device, 410...piezoelectric vibrator, 410A...first piezoelectric vibrator, 410B...second piezoelectric vibrator, 411...vibration portion, 412...support portion, 413...connection portion, 414...transmission portion, 420A...piezoelectric element, 420B...piezoelectric element, 420C...piezoelectric 420D...piezoelectric element, 420E...piezoelectric element, 420F...piezoelectric element, 420G...piezoelectric element, 490...urging member, 491...holding portion, 492...base, 493...spring group, 494...spring group, 600...control device, 1000...robot, 1100...base, 1200...manipulator, 1210...first arm, 1220...second arm, 1230...third arm, 1240... Fourth arm, 1250... fifth arm, 1260... sixth arm, 1270... end effector, 1310... first arm rotation mechanism, 1320... second arm rotation mechanism, 1330... third arm rotation mechanism, 1340... fourth arm rotation mechanism, 1350... fifth arm rotation mechanism, 1360... sixth arm rotation mechanism, 1370... end effector drive mechanism, 1400... robot control unit , A1...arrow, B...bearing, B1...arrow, Da...separation distance, Db...separation distance, O...rotation axis, Q1...acceleration region, Q2...constant velocity region, Q3...deceleration region, R1...first member, R2...second member, T1...time period, T2...time period, V1...drive signal, V2...drive signal, V3...drive signal, Vm...target maximum speed, Vr1...first speed, Vr2...second speed, θ0...rotational position, θ1...rotational position

Claims

1. A driven body that rotates around a rotation axis; a plurality of piezoelectric vibrators that transmit a driving force to the driven body to rotate the driven body; the plurality of piezoelectric vibrators include a first piezoelectric vibrator and a second piezoelectric vibrator that is distant from the rotation axis greater than the first piezoelectric vibrator; When accelerating the driven body, When the rotation speed of the driven body is less than a first speed, the driven body is rotated by a driving force of the second piezoelectric vibrator; A method for controlling a piezoelectric motor, comprising the steps of: rotating the driven body by a driving force of the first piezoelectric vibrator when the rotation speed of the driven body is equal to or higher than the first speed.

2. The piezoelectric vibrator has a vibration part that vibrates when a current is applied to a piezoelectric element, and a transmission part that contacts the driven body and transmits the vibration of the vibration part to the driven body, When transmitting a driving force to the driven body, the transmission part is elliptical vibrated.

2. The method for controlling a piezoelectric motor according to claim 1, wherein, when the driving force is not transmitted to the driven body, the transmission part is vibrated back and forth in a direction approaching and moving away from the driven body.

3. 3. The piezoelectric motor control method of claim 2, wherein when the driven body is accelerating, when the rotational speed of the driven body becomes equal to or greater than the first speed, the vibration of the first piezoelectric vibrator is changed from the reciprocating vibration to the elliptical vibration, and the vibration of the second piezoelectric vibrator is changed from the elliptical vibration to the reciprocating vibration.

4. The control method for a piezoelectric motor according to claim 3 , wherein the first piezoelectric vibrator and the second piezoelectric vibrator both undergo the elliptical vibration, and then the first piezoelectric vibrator undergoes the elliptical vibration and the second piezoelectric vibrator undergoes the reciprocating vibration.

5. In a state in which the first piezoelectric vibrator and the second piezoelectric vibrator are both elliptical vibrating, The method for controlling a piezoelectric motor according to claim 4 , wherein the driving force of the first piezoelectric vibrator is made smaller than the driving force of the second piezoelectric vibrator.

6. 3. The piezoelectric motor control method of claim 2, wherein when the driven body is decelerating, when the rotational speed of the driven body becomes equal to or lower than a second speed, the vibration of the first piezoelectric vibrator is changed from the elliptical vibration to the reciprocating vibration, and the vibration of the second piezoelectric vibrator is changed from the reciprocating vibration to the elliptical vibration.

7. The method for controlling a piezoelectric motor according to claim 2 , wherein when the driven body is decelerating, the vibrations of the first piezoelectric vibrator and the second piezoelectric vibrator are both made to be the elliptical vibration.

8. The method for controlling a piezoelectric motor according to claim 2 , wherein driving of the first piezoelectric vibrator and the second piezoelectric vibrator is stopped when the driven body is decelerating.

9. an interconnected first member and a second member; 9. A robot comprising: a piezoelectric motor whose drive is controlled by the method for controlling a piezoelectric motor according to claim 1, and which displaces the second member relative to the first member.

Images